Namibia's dunes pushing further north
The Namib sand sea, formed over centuries thanks to strong Atlantic winds, has been in motion for a million years, and the trend is increasing at an alarming rate.NASA's Earth Observatory now announced that newly evaluated Landsat 8 and 9 satellite photos taken between 2013 and 2022 (one per year) have shown faster movements.
The dunes in the restricted area of the southern Namib have migrated several kilometres to the north in recent decades, mainly driven by the persistent south-southwesterly winds.
Researchers from the Desert Research Institute and the Smithsonian used satellite observations from the Advanced Spaceborne Thermal Emission and Reflection Radiometer (ASTER) on NASA's Terra satellite to study dune movement over eight years. They found that the average movement speed of dunes there ranged between 7 and 32 meters a year.
Some smaller dunes moved much faster, even reaching up to 83 meters per year. Small dunes move faster than large ones simply because there is less material to move.
According to the Earth Observatory, large shifting dunes tend to maintain their shape, with researchers saying they move at an average of around nine meters per year.
"Tracking dunes with satellite imagery over years and decades shows that smaller dunes regularly appear and pass the larger crescent-shaped dunes," NASA's Earth Observatory said. “This makes the restricted area dunes some of the fastest moving dunes in the world."
There is a "very energetic wind regime with strong southerly winds, particularly in summer, making it one of the windiest desert regions in the world," said Nick Lancaster, a dune expert and research professor emeritus at the Desert Research Institute.
The dunes move because sand is eroded from the windward side of the dunes and deposited on the leeward (slip) side.